Patent Application
20060250434
Some ink-jet imaging systems, such as printers, use convection dryers to dry a marking fluid, such as ink, after it is deposited on a media sheet, such as paper. In some systems, the temperature of the heated air is not well correlated with the degree of marking fluid dryness and inadequate drying often results. Inadequate drying can result in output of wet media that can jam the imaging device or contaminate the media path with ink.
In the following detailed description of the present embodiments, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific embodiments that may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice disclosed subject matter, and it is to be understood that other embodiments may be utilized and that process, electrical or mechanical changes may be made without departing from the scope of the claimed subject matter. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the claimed subject matter is defined only by the appended claims and equivalents thereof.
For one embodiment imaging device 100, receives image data via interface 102. Imaging device 100 has a main controller 110, such as a formatter or a print engine controller, for interpreting the image data and rendering the image data into a printable image. The printable image is provided to a print engine 120 to produce a hardcopy image on a medium, such as a media sheet. For one embodiment, the imaging device 100 is capable of generating its own image data, e.g., a copier via scanning an original hardcopy image. Imaging device 100 also includes a drying system 130 for drying fluid, such as a marking fluid, deposited on the media sheets. For another embodiment, drying system 130 is controlled by controller 110. For another embodiment, drying system 130 is a subsystem of print engine 120.
Controller 110 includes a memory 140, e.g., a computer-usable storage media that can be fixedly or removably attached to controller 110. Some examples of computer-usable media include static or dynamic random access memory (SRAM or DRAM), read-only memory (ROM), electrically-erasable programmable ROM (EEPROM or flash memory), magnetic media and optical media, whether permanent or removable. Memory 140 may include more than one type of computer-usable storage media for storage of differing information types. For one embodiment, memory 140 contains computer-readable instructions, e.g., drivers, adapted to cause controller 110 to format the data received by imaging device 100, via interface 102 or by scanning, and computer-readable instructions to cause imaging device 100 to perform the various methods described below.
A voltage sensor 280 is connected across heating element 240, and a current sensor 285 is connected in series with voltage sensor 280 and heating element 240. A power measurement block 290 is connected to current sensor 285 and voltage sensor 280 and to drying system controller 270. For one embodiment, current sensor 285 may be a calibrated sense resistor having a predetermined resistance value connected in series with heating element 240, and the current through current sensor 285 and thus through heating element 240 is determined by measuring a voltage drop across the sense resistor and using Ohms law with the measured voltage drop and the predetermined resistance value.
Power measurement block 290 receives inputs respectively indicative of the current flowing through heating element 240 and the voltage drop across heating element 240. For one embodiment, power measurement block 290 includes an analog-to-digital (A/D) converter for digitizing these inputs. For some embodiments, power measurement block 290 is integrated within drying system controller 270. Power measurement block 290 includes a signal multiplier that multiplies the inputs indicative of the current flowing through heating element 240 and the voltage drop across heating element 240 for computing the actual power supplied to heating element 240 during a time relatively short time interval. For one embodiment, power measurement block 290 sends a signal indicative of the actual power to drying system controller 270 during a relatively short time interval.
In operation, for one embodiment, drying system controller 270 instructs power controller 260 to allow power to be supplied from power supply 250 to heating element 240. Moreover, drying system controller 270 activates fan 234 for some embodiments. Signals indicative of the current flowing through heating element 240 and the voltage drop across heating element 240 are then respectively sent from current sensor 285 and voltage sensor 280 to power measurement block 290. Power measurement block 290 multiplies the signals together to compute the power supplied to heating element 240 during a relatively short time interval and sends a signal indicative of the power supplied to heating element 240 to drying system controller 270. For one embodiment, a power value is computed at power measurement block 290 and sent to drying system controller 270 for each of a plurality of time intervals.
Drying system controller 270 then determines the energy Ei delivered to the marking fluid deposited on a media sheet for drying (or vaporizing) the marking fluid deposited on a media sheet for each of the time intervals from
Ei=Pi*(η*Δti) (1)
where Pi is the power value computed at power measurement block 290 for the ith time interval, Δti is the length of the ith time interval, and η is an efficiency value, such as an overall drying efficiency, that accounts for losses in the dryer 232, heat lost into the media, the media type, etc. The energy delivered to the marking fluid for a number of time intervals can then be determined by summing the energies delivered during each of the number time intervals over the number of time intervals. For one embodiment, drying system controller 270 forms a running total of the energy delivered to the marking fluid deposited on the media sheet by adding the energy delivered during each successive time interval to the energy delivered to the marking fluid during the preceding time intervals. For example, for N time intervals, the running total of the energy is formed by adding an energy EN delivered during the Nth time interval to the energy delivered during the N−1 preceding time intervals as follows:
Erun=(E1+E2+ . . . +EN−1)+EN (2)
For one embodiment, drying system controller 270 determines a volume of ink deposited on a media page. For another embodiment, the volume of ink deposited on the media page is determined from the image data, e.g., a bitmap or the like, corresponding to the image to be printed that is sent to the main controller from a host computer. Drying system controller 270 then determines the total amount of energy to be used to dry the marking fluid (or vaporize liquid contained in the making fluid) deposited on the media sheet based on the determined volume of ink and thermophysical properties of the marking fluid. For some embodiments, determining the total amount of energy to be used to dry the marking fluid deposited on the media sheet based on the determined volume of ink includes going into a look-up table corresponding to the particular media type and/or marking fluid type with the determined volume of ink and retrieving the amount of energy to be used to dry the marking fluid corresponding to that volume and that media type. For one embodiment, the look-up table may be contained in memory 140.
Drying system controller 270 then determines whether Erun is sufficient for drying the marking fluid. For one embodiment, this is accomplished by comparing the total amount of energy to be used for drying the marking fluid to Erun after each time interval. When Erun is substantially equal to or greater than the total amount of energy to be used for drying the marking fluid, drying system controller 270 instructs power controller 260 to stop power from being supplied, or reduce power being supplied in some embodiments, from power supply 250 to heating element 240. Otherwise, the power continues to be supplied to heating element 240 for additional time intervals as appropriate, and Erun is updated by adding the energy supplied during the additional time intervals and compared to the amount of energy to be used for drying the marking fluid.
For various embodiments, the efficiency η can be determined experimentally for various fan speeds, dryer geometries, media types, relative humidity, marking fluid type, etc. For one embodiment, this may involve depositing a predetermined amount of marking fluid on a media sheet and drying the ink for a preselected time period at a preselected power, where the length of the preselected time period may or may not be sufficient for completely drying the marking fluid. At the end of the preselected time period, the media sheet is weighed to determine the amount of drying, i.e., the amount marking fluid evaporated. The efficiency η can then be determined from
η=E/(PΔt) (3)
where E is the energy that goes into evaporating the marking fluid, calculated from thermophysical properties of the marking fluid and the amount of marking fluid evaporated, P is the preselected power, Δt is the length of the preselected time period, and PΔt is the energy input to the dryer during Δt. Note that an average power PAV can be used for P, where the average power is determined from
PAV=(P1Δt1+ . . . +PMΔtM)/(Δt1+ . . . +ΔtM) (4)
and where (Δt1+ . . . +ΔtM)=Δt and P1, . . . , and PM are the powers measured during the respective time intervals and corresponding to Δt1, . . . , and ΔtM. For one embodiment, the powers can be measured as described above.
Note that drying system controller 270 may select an efficiency based on the particular a fan speed, dryer geometry, relative humidity, marking fluid type, and/or media type, for various embodiments. For these embodiments, drying system controller 270 would receive inputs indicative of fan speed, dryer geometry, relative humidity, marking fluid type, and/or media type. For one embodiment, the fan speed, dryer geometry and/or marking fluid type may be fixed. For another embodiment, the imaging device may include sensors for sensing the media type and/or the relative humidity. Since it may not be practical to obtain efficiency data for every possible relative humidity, drying system controller 270 may interpolate an efficiency at the measured relative humidity of the surroundings from efficiencies at other relative humidities prestored in a look-up table, e.g., contained in memory 140, for some embodiments. This could also be done for fan speed and/or marking fluid type for one embodiment.
Although specific embodiments have been illustrated and described herein it is manifestly intended that the scope of the claimed subject matter be limited only by the following claims and equivalents thereof.
